Output buffer circuits are utilized extensively in Electrical Programming Read Only Memory (EPROM) devices for providing an output voltage responsive to an input signal. New EPROM devices, such as the Am27C020 and Am27LV020, manufactured by Advanced Micro Devices, Incorporated are capable of storing information at low voltages. What is meant by low voltage in the context of this application is between 2.7 and 3.6 volts.
Speed is a very important component of output buffer circuits at these low voltages. Hence, in designing these devices, particularly the output buffer circuit, it is important that they operate efficiently at these low voltages. However, it is known that there are problems when programming a low voltage EPROM circuit. For example, it is known that many existing programmer circuits are very poorly grounded in use and when the program verify mode is used, a EPROM could fail.
In addition, ground bounce or ringing on the output device has been a significant problem in programming these types of circuits using traditional programming techniques. Typically, 6 volts or more are required to ensure that the EPROM is properly programmed. Hence, one way to solve the problem is to program the devices at the lower voltages to prevent ringing. However, to program the devices at lower voltages would require significant modifications to existing programming techniques.
Another way of solving the problem would be to utilize a circuit design which would minimize the ground bounce problem associated with programming these low voltage EPROM devices. But in so doing, the performance characteristics of the device would be significantly reduced during normal low voltage operation. Hence, the device would no longer be optimized for speed and would not perform efficiently. Hence, what is needed is an improved output buffer circuit that would allow for the high speed performance characteristic associated with low voltage EPROM devices but at the same time minimizing the noise problems associated with the programming of such a low voltage EPROM device.
The present invention provides circuitry for addressing the above-mentioned need.